Use of L-carnitine and its alkanoyl derivatives as osmotic agents in solutions for medical use

ABSTRACT

The use of L-carnitine and its alkanoyl devivatives, optionally in the form of a pharmaceutically acceptable salt, as osmotic agents in the preparation of solutions for medical use, particularly for peritoneal dialysis, is described.

This application is the US national phase of international applicationPCT/IT99/00317 filed 11 Oct. 1999, which designated the US.

The invention described herein relates to the use of L-carnitine and itsalkanoyl derivatives, optionally in the form of a pharmaceuticallyacceptable salt as osmotic agents in solutions for medical use,particularly in peritoneal dialysis.

BACKGROUND OF THE INVENTION

Patients suffering from end-stage renal disease (or ESRD) must eitherundergo dialysis therapy or be submitted to a kidney transplant. Boththerapeutic interventions are extremely demanding, both from the pointof view of the quality of life of the patient and in terms of socialcosts. For a review of dialytic therapy see, for example, Pastan S. andBailey J. in the New England Journal of Medicine, 14 May 1998, pp.1428-1436, incorporated herein for reference in its entirety.

Dialytic therapy comprises two types of treatment, namely peritonealdialysis and haemodialysis. There are major differences between the twotypes of dialysis, such as, in the case of haemodialysis, the cost ofthe therapy, the need for dedicated departments with expensive equipmentand qualified staff, and the quality of life of the patient. Peritonealdialysis, on the other hand, enjoys greater favour on account of itssimplicity of execution, which can be handled by the patient himself inthe form of self-medication. In Italy, for example, 15% of dialysispatients use peritoneal dialysis, which is practically the same as inthe USA (16%), while the percentages of patients on peritoneal dialysisare higher in Canada (38%) and the United Kingdom (52%), and get up toas much as 90% in Mexico. The reason for these different rates is alsoto be attributed to the lower cost of peritoneal dialysis as compared tothe cost of haemodialysis which not all national health systems areprepared to bear. We should, however, not overlook the fact thatperitoneal dialysis allows the patient to maintain a less constrainedlife-style, since the dialysis session can be planned with a certainmeasure of autonomy in the course of the person's normal activities. Inaddition, automatic devices also allow dialysis during the hours of thenight.

Despite this, the choice between the two types of dialysis is not a freeone; for instance, peritoneal dialysis is indicated for patients withcardiac insufficiency or unstable angina who cannot support thealterations of blood flow and/or arterial blood pressure that accompanythe haemodialysis session (see reference cited above).

One can postulate a therapeutic progression for the ESRD patient whichstarts with peritoneal dialysis, proceeds via haemodialysis and finallyreaches a stage where a kidney transplant is needed.

Peritoneal dialysis is not without disadvantages and unwanted adverseeffects. These drawbacks can be placed in two distinct, even if related,categories, namely adverse clinical effects and technological problems.The purpose of the invention described herein is to remedy thesedisadvantages and adverse effects.

In the typical execution of a peritoneal dialysis session, a plasticcatheter is implanted in the peritoneal cavity and anchored to thesubcutaneous tissues. A dialysis solution contains physiological amountsof sodium, calcium, magnesium, compatible physiological buffer and anon-toxic osmotic agent, of such a nature as to make the solutionhyperosmolar as compared to the plasma. The solution is infused via thecatheter into the peritoneal cavity where it then remains for severalhours. During this time, the peritoneal membrane exchanges solutes bydiffusion in such a way as to obtain replacement with fresh fluid. Giventhat renal function decreases in the first few years of dialysis, thedose of dialysis fluid to be exchanged increases in the course of time.

Peritonitis is the serious complication that occurs most frequently.Other types of complications are losses of amino acids and albumin,incompatibility of the dialysis solution, volume effects in theperitoneal cavity, metabolic consequences, symptoms affecting thedigestive tract, reduced appetite and others (for a review see C. M.Mion, R. and Gokal and N. P. Mallick, Lancet, 1999; 353; 823-28).

One of the most pressing problems in the peritoneal dialysis sector isthe choice of a suitable osmotic agent.

The requisites of an ideal solution for peritoneal dialysis include:

supplying the nutritional requirement and avoiding adverse metaboliceffects;

ensuring minimal absorption of the osmotic agent, which, in any case,must be non-toxic;

being capable of correcting acidosis and having a physiological pH;

in addition to considerations with technological implications, such asapyrogenicity, absence of metals and residues of synthetic materials,the solution must also inhibit bacterial and fungal growth, must notdamage the immune defences and must be inert in relation to theperitoneal membrane. A typical solution for peritoneal dialysis containsglucose in various concentrations as an osmotic agent, and variousamounts of lactate (which has replaced acetate owing to problems ofintolerance on the part of the patient), sodium, potassium and calcium.Buffer systems have also been studied in an attempt to solve the problemof sterilization and stabilization of the solution.

As regards the sterilization aspect, this is a critical technologicalproblem; in fact, heat sterilization, commonly used in the sector ofsolutions for medical use, causes degradation of glucose, withconsequent production of toxic secondary derivatives, such as aldehydesand 5-hydroxy-methylfurfural. Traditionally heat sterilization of thesolution containing glucose (also indicated as dextrose) is done at a pHbetween 5.0 and 5.5, precisely in order to avoid caramelization of theglucose. The acid pH leads to further problems for the patient using thesolution, such as, for example, abdominal pain and sclerosis of theperitoneal membrane, which entails a reduction of the elimination ofsolutes (Schmidt et al., Arch. Int. Med., 141; 1265-1266, 1981).

The purpose of the invention described herein is also to provide asolution to the complex problems related to the use of glucose as anosmotic agent in solutions for peritoneal dialysis.

Glucose is extensively used owing to its great availability on themarket and its low cost. It is a relatively safe substance, but its useat high concentrations and its prompt absorption lead to shortultrafiltration times, and metabolic complications, such ashyperinsulinaemia, hyperlipidaemia, and weight gain. In addition,hyperosmolarity and low pH can damage the mesothelium and macrophages.Moreover, the potential glycosylation of stromal proteins leads tofurther damage to the peritoneum. Also reported is the inhibition ofphagocytosis, bactericidal activity and the synthesis of LTB₄ inperipheral blood neutrophils. In continuous ambulatorial peritonealdialysis (CAPD), where the application time can be as much as 6 hours ormore, the glucose concentrations are very high to be able to maintainthe ultrafiltration capacity. For a review of the biocompatibility ofsolutions for peritoneal dialysis see C. J. Holmes in PeritonealDialysis International, Vol. 13, pp. 88-94, 1993.

To overcome the problems created by the use of glucose as an osmoticagent in peritoneal dialysis, the state of the art directs experts inthe field towards two distinct types of solution:

1) the use of low-molecular-weight osmotic agents, capable of sustainingultrafiltration with minimal metabolic effects, without, however,altering the ultrafiltration profile;

2) the use of high-molecular-weight osmotic agents in an attempt to acton both factors.

Of the various low-molecular-weight agents proposed, to date onlyglycerol and mixtures of amino acids would appear to be of a certainclinical interest. In Italy, for example, a 1.1% multi-amino-acidsolution is being marketed by Baxter under the trade mark Nutrineal® PD2and PD4.

These proposed alternatives to glucose are not problem-free; othersaccharides have metabolic effects: for example, fructose gives rise tohypertriglyceridaemia and hyperosmolarity, sorbitol hyperosmolarity andaccumulation, xylitol lactic acidosis and hyperosmolarity; glycerol iswell tolerated, but its ultrafiltration capacity is short-lasting and italso causes hyperosmolarity, while an adverse effect on phagocytes hasalso been reported (de Fijter CWH et al., Advances in ContinuousAmbulatorial Peritoneal Dialysis, Toronto, Peritoneal DialysisPublication, 1991, 154-7). Amino acids, though useful in undernourishedpatients, give rise to acidosis and to an increase in the nitrogen load,which is contraindicated in an uraemic patient. On the other hand,high-molecular-weight osmotic agents present a whole series ofdisadvantages of their own, such as possible immunogenicity in the caseof peptides, absorption, intraperitoneal bleeding (demonstrated in rats)and ultrafiltration in the case of dextrans (MW 60-200 kDa),cardiovascular instability, peritoneal damage and haemorrhage in thecase of polyanions and cations (MW 40-90 kDa), prolonged half-life,immunogenicity, allergenicity and high viscosity of the solution in thecase of gelatines (MW 20-390 kDa) and maltose retention in the case ofglucose polymers.

Unfortunately, the adverse effects of solutions for peritoneal dialysisdo not stem only from the osmotic agent chosen, but also from othercomponents of the solutions. Lactate, for example, when combined withthe low pH of the solution, which is necessary in order to be able toperform sterilization, suppresses various functional activities of theperipheral and peritoneal leukocytes and inhibits the production of IL-6and TNFα by mononuclear cells.

In his review of osmotic agents, Gokal concluded in 1990 that at thattime there was no osmotic agent capable of replacing glucose (Coles G A,Davies M, Williams J D (eds): CAPD: Host Defence, Nutrition andUltrafiltration. Contrib. Nephrol., Basel, Karger, 1990, vol. 85, pp.126-133).

An enormous effort is being made to find an alternative osmotic agent toglucose, meeting or at least coming close to meeting the requisites ofthe “ideal” solution. Among the numerous patent references, we shouldcite patent JP 11071286, filed in the name of the Terumo Corp., whichdescribes a solution where the osmotic agent consists in a mixture ofglucose and maltose in molar ratios of 1:0.05-5 and with an osmoticpressure of 280-600 mOsm/kg at pH 6.0-7.5, with enhanced water removalcharacteristics and reduced glucose absorption. For obese, diabeticpatients, the same company supplies a complex osmotic agent, made up ofN-acetylamine acid (L-amino acid), N-acetyl-D-glucosamine, glucuronicand/or ascorbic acid (patent JP 11071273). Mixtures of saccharides withhexavalent alicyclic alcohols, hexonic acid and sacchric acid aredescribed in patent JP 11049671, filed in the name of Baxter Int. Inc.Patent application WO 9901144, filed by Allied Therapeutics Ltd.,describes synthetic hydrogenated di- and trisaccharides. Patent MX9601855, filed by Trevino, uses dextran 60. Baxter again, in patent JP10094598, proposed non-reducing oligosaccharides or polysaccharidescontaining from 3 to 12 residues. In patent application WO 9801141,filed by Bieffe Medital SpA, the use of glycosaminoglycans, devoid ofanticoagulant or haemorrhagic activity, is described. U.S. Pat. Nos.5,629,025, 5,589,197 and 5,631,025, filed in the name of BaxterInternational Inc., describe solutions for peritoneal dialysis with alow sodium content, for which substances containing at least one aminoacid or polypeptide, or a polyglucose, are envisaged as osmotic agents.The University of Missouri supplies chemically crosslinked gelatine asan osmotic agent to partially or wholly replace glucose (U.S. Pat. No.4,604,379). Starch hydrolysates are described in U.S. Pat. No.5,837,060, filed in the name of Roquette Freres. Patent JP 7323084,filed by Morishita Roussel KK and Ajinomoto Co. Inc., describes the useof trehalose to prepare neutral solutions to replace glucose. See alsoU.S. Pat. No. 4,761,237.

Examining in greater detail the low-molecular-weight osmotic agents towhich the present invention refers, the state of the art providesteachings directed to the use of amino acids or short peptides, whichare advantageous from the point of view of the nutritional support ofundernourished patients. Baxter International Inc., under its U.S. Pat.No. 5,776,503, supplies a mixture of amino acids, which is highlycomplex but, despite its very high cost, has yet to be surpassed by themany alternatives proposed. U.S. Pat. No. 5,780,438, filed in the nameof Giltech Limited, describes a stable solution, where the osmotic agentconsists of a mixture of peptides obtained from the proteolysis ofcasein or whey proteins. U.S. Pat. No. 5,869,444, filed in the name ofResearch Corporation Technologies, extensively discusses thealternatives to glucose and directs the experts in the field towardslow-molecular-weight osmotic agents of an amino-acid nature. However,though admitting the nutritional benefit, mentioned earlier, theinventors stress the disadvantage of the high cost, and the increasednitrogen load in the blood. Thus, in the cited patent, they propose theuse of oligopeptides (300-2000 Da) derived from the enzymatic hydrolysisof high-quality proteins, such as whey, which are advantageous both fromthe functional point of view of the dialysis and from the nutritionalpoint of view. In this patent, however, the need is perceived for a verythorough and carefully controlled hydrolysis and separation process inorder to avoid the risk of high-molecular-weight components, potentialantigens or allergens. Among the protein sources, those mentionedinclude collagen, the use of which today is, however, questionable owingto problems of prion contamination (BSE, scrapie), milk proteins, butnot casein, and others. In the course of the description, the inventorsadmit a series of difficulties in assuring the quality of the hydrolysisprocess.

In relation to other aspects of peritoneal dialysis, DE 19748290, WO991762, JP 10330270, WO 9852599, WO 9850060, CA 2219822, WO 9917762 andU.S. Pat. No. 5,827,820 are cited.

All documents cited are incorporated herein for reference in theirentirety.

ABSTRACT OF THE INVENTION

It has surprisingly been found that L-carnitine, or, alternatively, oneof its lower alkanoyl derivatives, or L-carnitine in combination withits lower alkanoyl derivatives, is useful as an osmotic agent in thepreparation of solutions for peritoneal dialysis, and in general as anosmotic agent for solutions for medical use.

One subject of the invention described herein is the use of L-carnitineand its lower alkanoyl derivatives, where what is meant by loweralkanoyl derivative is a straight or branched aliphatic acylic residuewith from 2 to 8 carbon atoms, optionally in the form of apharmaceutically acceptable salt, as an osmotic agent in solutions formedical use, particularly for the preparation of solutions forperitoneal dialysis. Another subject of the present invention consistsin solutions for medical use characterised in that the osmotic agent isL-carnitine or one of its alkanoyl derivatives, as defined above,optionally in combination with one another or with one or more knownosmotic agents.

L-carnitine and its lower alkanoyl derivatives are known to have varioustherapeutic uses. In particular, U.S. Pat. No. 4,327,167, filed in thename of the applicant, describes the use of alkanoyl carnitines, asdefined above, in a therapeutic method for the treatment of chronicuraemic patients undergoing regular dialysis. Also described arepolysaline solutions for haemodialysis containing an alkanoyl carnitine.Patent EP 0793962, filed in the name of the applicant, describes the useof propionyl L-carnitine for the preparation of a medicine useful forthe selective treatment of chronic obliterating atherosclerosis(claudicatio intermittens). Patent IT 1155772, filed in the name of theapplicant, describes the use of alkanoyl L-carnitine in the therapy ofmyocardial anoxia, ischaemia, arrhythmia syndromes and heart failure.U.S. Pat. No. 4,255,449, filed in the name of the applicant, describesthe use of L-carnitine in the treatment of dyslipidaemias. Patentapplication WO 9906039, filed in the name of the applicant, describesthe use L-carnitine and its alkanoyl derivatives in combination withpolycosanols for the treatment of dyslipidaemias. There are numerousdescriptions of combinations of L-carnitine and alkanoyl derivativeswith other active ingredients, e.g. gamma-linoleic acid (see WO 9841113)for the treatment and prevention of the side effects of diabetesmellitus, particularly peripheral neuropathy.

U.S. Pat. No. 4,272,549 teaches the use of particular administrationregimens of L-carnitine combined orally and intravenously to combatpost-dialysis syndrome in uraemic patients undergoing regularhaemodialysis treatment.

U.S. Pat. No. 4,237,167 teaches the use of particular administrationregimens of acyl L-carnitine combined orally and intravenously to combatpost-dialysis syndrome in uraemic patients undergoing regularhaemodialysis treatment.

Patent application WO 9907419, filed in the name of Gupta, describescompositions for dialysis containing an effective amount of at least onevitamin selected from the group consisting of folic acid, vitamin B₆,thiamine, vitamin B₁₂, and optionally vitamin C and/or carnitine. Thepurpose of these preparations is to compensate for the loss of vitaminsto which patients on either haemodialysis or peritoneal dialysis aresubject. The effective amounts are indicated in the description. In thecase of free L-carnitine, an amount less than 50 μmol/l is specified forthe dialysed patient during each dialysis session for the prevention ofvitamin and carnitine deficiencies. The preferred concentrations rangefrom 50 to 300 μmol/l. Thus, the amount of L-carnitine present in thesolutions described by Gupta is less than the amount necessary forL-carnitine to act as an osmotic agent.

The advantages of using L-carnitine or one of its alkanoyl derivatives,as defined above, are multiple. The replacement of glucose byL-carnitine or one of its alkanoyl derivatives eliminates the adverseeffects described above. Furthermore, the carnitines (meaningL-carnitine or its alkanoyl derivatives as defined in the inventiondescribed herein) are compatible with the bicarbonate buffer, andtherefore obviate the disadvantage of having to use solutions at belowphysiological pH, such as the pH 5.0 or 5.5 typical of glucosesolutions.

The use of carnitines, particularly L-carnitine, acetyl L-carnitine andpropionyl L-carnitine, is additionally advantageous compared to otherknown osmotic agents because the carnitines are non-toxic, welltolerated substances with no adverse effects at the doses describedbelow. Unlike the amino acids, the carnitines play no part in proteinmetabolism and thus do not aggravate the nitrogen load of the uraemicpatient. As regards the difference from high-molecular-weight osmoticagents, the advantage is immediate: the carnitines are naturalsubstances present in living organisms, particularly mammals, includingman. For this reason, the risk of introducing xenobiotic substances intothe body is eliminated.

Moreover, the use of carnitines as osmotic agents provides the dialysedpatient with the amount of L-carnitine necessary to compensate for thecarnitine losses which occur during the dialysis session. For data oncarnitine levels in patients undergoing CAPD, see Kidney Int. 1996January; 49(1): 158-62 and Perit. Dial. Int. 1993; 13 Suppl 2.

A further advantage of the application of the invention described hereinis that carnitine, when used as an osmotic agent, not only compensatesfor the carnitine losses, but is also capable of exerting its owntherapeutic effects in a series of diseases related to renalinsufficiency, such as, for example, the diseases described in theabove-mentioned patents.

The invention will now be described in detail also with the aid ofexamples. Further subjects of the invention described herein, with theirrespective advantages, will be apparent to experts in the field to whichthe present invention pertains.

DETAILED DESCRIPTION OF THE INVENTION

What is meant by lower alkanoyl is an acyl group with from 2 to 8 carbonatoms, preferably from 2 to 6, such as acetyl, propionyl, butyryl,isobutyryl, valeryl, isovaleryl, 2-methyl-butyryl,2,2-dimethylpropionyl, hexanoyl, heptanoyl, octanoyl and all theirpossible isomers.

The invention described herein envisages the use of carnitines as innersalt. If deemed suitable, one of their pharmaceutically acceptable saltscan be used. What is meant by pharmaceutically acceptable salt ofL-carnitine or of an alkanoyl L-carnitine derivative is any salt of thelatter with an acid which does not give rise to unwanted toxic or sideeffects. These acids are well known to pharmacologists and to experts inpharmaceutical technology.

Examples of pharmaceutically acceptable salts of L-carnitine or alkanoylL-carnitines, though not exclusively these, are chloride, bromide,orotate, acid aspartate, acid citrate, acid phosphate, fumarate and acidfumarate, maleate and acid maleate, acid oxalate, acid sulphate, glucosephosphate, tartrate and acid tartrate. The preferred salts are thosewith fumarate, aspartate, citrate and maleate.

Also the subject of the invention described herein are solutions forperitoneal dialysis, both in the form of ready-to-use solutions and inthe form of concentrates to be diluted at the time of use, containing anosmotic agent according to the present invention.

The dosages, posology and treatment regimen in general will bedetermined by the primary care physician according to his knowledge ofthe case, the patient's condition and the extent of the disease to betreated.

In a first preferred realization, in the invention described hereinL-carnitine, inner salt, is used.

In a second preferred realization, carnitine is present in the form of asalt with fumaric acid. Though not wishing to be bound by any theory,the applicant believes that the fumarate salt may be particularlyadvantageous for supplying the energy requirement of the dialyzedpatient. Fumarate, in fact, is an energy substrate which is useful inthe treatment of organ ischaemia. The applicant has demonstrated theefficacy of L-carnitine fumarate in the treatment of organ ischaemia,particularly ischaemic heart disease, as described in patent application99RM0003328, incorporated herein for reference in its entirety.

In a third realization of the invention described herein, a combinationof L-carnitine and acetyl L-carnitine is used. This combination isadditionally advantageous to provide the patient with an acetylL-carnitine supplement.

In the description of the possible realizations of the invention, whatis meant by carnitine is L-carnitine, as inner salt, or a salt with apharmaceutically acceptable acid, as described above, alone or incombination with one of its alkanoyl derivatives as inner salt, or as asalt with a pharmaceutically acceptable acid, or one of its alkanoylderivatives, as inner salt or a salt with a pharmaceutically acceptableacid.

In a first aspect of the present invention, carnitine is used as anosmotic agent as a total substitute for glucose.

The carnitine concentrations are those sufficient for it to act as anosmotic agent and concentrations up to a physiologically tolerablemaximum are envisaged. It is understood that the carnitine concentrationwill be such as to ensure a satisfactory effect for the uses envisagedfor the present invention. In particular, it is considered satisfactorythe obtained which can be considered a therapeutic effect in the contextof peritoneal dialysis.

Where not otherwise specified, the concentrations are understood to beweight/volume (w/v).

Examples of concentrations are approximately 0.5 to approximately 10%,preferably approximately 0.7 to approximately 7%, and more preferablyfrom approximately 1 to 5%. In a typical realization of the presentinvention, the carnitine concentrations are those normally used forglucose in commercial preparations, namely from 1.5 to 4.25%.

It is understood that experts in the field will be capable ofdetermining effective concentrations according to the type of solutionused. Examples are concentrations starting from approximately 0.5%.

If so required, alternatively, carnitine can be used as a partialsubstitute for glucose. The respective carnitine and glucoseconcentrations can be freely varied, provided that a satisfactory effectis obtained in terms of the uses envisaged for the present invention.Examples of combinations with glucose are 4.0% glucose-0.25% carnitine;1.0% glucose-0.5% carnitine; 0.5% glucose-1.0% carnitine; 0.25%glucose-4.0% carnitine. The 0.5% glucose-1.0% carnitine combination ispreferred.

Other possible realizations of the invention consist in a combination ofcarnitine as an osmotic agent with other known osmotic agents; forexample, preferred combinations are those with amino acids, such as theformulations already present on the market, or with the dipeptidesand/or polypeptides of the above-mentioned patents. One particularlyadvantageous realization is the use of carnitine in the twin bagsdescribed in patent DE 19748290, which uses bicarbonate buffer. It isalso useful to increase the dose of carnitine, particularly L-carnitine,in the solutions described in WO 9907419 up to a concentration which iseffective as an osmotic agent.

In another possible realization, the osmotic agent according to thepresent invention is used in combination with the osmotic agentsdescribed in U.S. Pat. No. 5,827,820, filed in the name of BaxterInternational Inc.

The use of the osmotic agent according to the present invention is alsoenvisaged in combination with high-molecular-weight osmotic agents, suchas, for instance, those described in the above-cited references, andparticularly with icodextrin.

In a particular realization of the present invention, a surfactantnormally used in this field is added to the peritoneal dialysissolution. Specific mention is made of palmitoyl L-carnitine.

One specific subject of the present invention consists in solutions formedical use characterized in that the osmotic agent is L-carnitineand/or its alkanoyl derivatives, in which the alkanoyl is a straight orbranched aliphatic residue with from 2 to 8 carbon atoms, optionally inthe form of a pharmaceutically acceptable salt. A particular subject ofthe present invention consists in solutions for peritoneal dialysis.

As regards those aspects pertaining to industrial applicability, thesolutions which are the subjects of the present invention will becontained in suitable containers for peritoneal dialysis, generally bagsmade of suitable material compatible with medical use. Containers forperitoneal dialysis are known to experts in the field and do not requireany particular description, the reader being referred to the specificliterature and to the general knowledge of the technical field to whichthe invention pertains. Examples are bags with a single chamber ormultiple chambers, e.g. a double chamber, or separate bags containingdifferent solutions to be mixed at the time of use by means of automaticequipment. Containers for peritoneal dialysis containing a solutionaccording to the present invention are covered by the protectionafforded by the present patent application.

The invention described herein is now described with the aid ofexperimental tests permitting the implementation of the the realizationpreferred. It is fully understood that equivalent realizations comingwithin the framework of the present invention can be implemented by theperson having ordinary skill in the field, availing himself only of hisown general knowledge, even by the trial and error method, without anyneed for further description on the part of the present invention.

In-vitro Transport Studies

Fluid transport in vitro was performed using tubes consisting ofsemipermeable cellulose membranes containing the various differentdialysis solutions.

Buffer solutions were added with scalar concentrations of carnitine(0.5, 1.0 and 1.5%) in bicarbonate buffer (30 mM) and NaCl (100 mM) atpH 7.2. A 1.5% glucose solution was used as a reference.

The composition of the buffer solution is as follows: sodium 134 mmol/l,calcium 1.75 mmol/l, magnesium 0.5 mmol/l. The solutions containingglucose were buffered at pH 5.5 with 35 mmol/l of L-lactate. Thesolutions containing carnitine were buffered as for glucose at pH7.0-7.6 with 34 mmol/l of bicarbonate. Ten ml of the various dialysissolutions were placed in the tubes and the tubes were suspended in a1liter graduated cylinder filled with a 0.9% NaCl solution. The salinebath was recycled at a rate of 500 ml/min with direct flow along themain axis of the dialysis tube using an infusion pump. The amount offluid recovered inside the tube was determined gravimetrically afterremoving the fluid adhering to the walls of the membrane with a sheet ofabsorbent paper. The tube was then put back inside the cylinder andsubmitted to successive weight measurements at 15, 30, 45, 60, 90, 120,180, 240, 300 and 360 minutes.

Table 1 gives the increase in weight of the fluid recovered the dialysissolution in the course of time.

TABLE 1 Fluid transport induced by 10 ml of fluid containing differentconcentrations of carnitine or glucose. Carnitine Times Carnitine 0.5%1.0% Carnitine 1.5% Glucose 1.5% (min) (g fluid) (g fluid) (g fluid) (gfluid) 15 0.02 ± 0.01 0.07 ± 0.02 0.10 ± 0.01 0.09 ± 0.02 30 0.06 ± 0.010.13 ± 0.02 0.26 ± 0.03 0.19 ± 0.03 45 0.10 ± 0.03 0.20 ± 0.03 0.30 ±0.02 0.27 ± 0.02 60 0.12 ± 0.02 0.22 ± 0.03 0.35 ± 0.04 0.31 ± 0.04 900.17 ± 0.03 0.33 ± 0.03 0.48 ± 0.04 0.41 ± 0.04 120 0.19 ± 0.02 0.36 ±0.03 0.54 ± 0.04 0.47 ± 0.04 180 0.21 ± 0.03 0.42 ± 0.04 0.66 ± 0.040.54 ± 0.04 240 0.27 ± 0.02 0.49 ± 0.03 0.77 ± 0.05 0.59 ± 0.04 300 0.29± 0.02 0.51 ± 0.03 0.77 ± 0.04 0.63 ± 0.05 360 0.27 ± 0.03 0.48 ± 0.040.74 ± 0.05 0.62 ± 0.04

The values are means (n=3)±S.D. of 3 different experiments.

The weight of the dialysis tube increases progressively over time as afunction of the different carnitine concentrations. The plateau isreached for all concentrations assayed at 240 minutes. The trend of thesamples containing 1.5% glucose is comparable to that of the samplescontaining 1.5% carnitine.

In-vivo Experiments

The peritoneal dialysis experiment was conducted in male Sprague-Dawleyrats weighing 500-600 g (Charles River) maintained on a standard dietwith water ad libitum. The animals were anaesthetized with anintraperitoneal injection of inactin (100 mg/kg) and were placed on anoperating table at controlled temperature. The animals were submitted toa tracheostomy to cannulate the left jugular vein with a PE50 medicalsilicone tube. Thirty minutes after administration of the anaestheticthe animals were infused with a saline solution at a rate of 2.3 ml/hthroughout the period of the experiment. The dialysis solution (15 ml),after preheating to 37° C., was inoculated into the peritoneal cavitywith a 15 teflon needle-cannula 1 h after administration of theanaesthetic. The amount of fluid injected was determined by weighing thesyringe before and after injection of the fluid, using an electronicscale. At the end of each analysis period (2, 4 and 6 h), incisions weremade in the rats' abdomens with an acusector and all the fluid presentin the peritoneum was aspirated with a 1 ml syringe. After removing thesurface fluid, the intestines were carefully shifted from the abdominalcavity to collect the residual fluid remaining on the dorsal wall. Thefluid recovered was placed in a beaker and weighed. The change in weightcompared to time 0 represented the amount of fluid recovered from theperitoneal solution injected.

A series of in-vivo experiments was conducted according to theexperimental model described above in order to evaluate the transportability of various dialysis fluids containing carnitine.

The data relating to initial and final weight of the fluid recoveredfrom the peritoneum of the animals at the different analysis times wereused to calculate the percentage increase in volume in each animal.

Table 2 gives the data for an experiment in which glucose was used atdifferent concentrations (1.5, 2.5 and 4.25%) as the dialysis fluid.These hyperosmolar solutions constitute our control data since they arethose commonly used in clinical practice.

TABLE 2 Percentage changes in fluid volume recovered from rats submittedto peritoneal dialysis with 15 ml of solution containing differentconcentrations of glucose. % increase in % increase in % increase involume volume volume Solutions (2 h) (4 h) (6 h) Glucose 1.5% 21.1 ± 1.521.5 ± 1.9 21.7 ± 1.6 Glucose 2.5% 35.2 ± 1.4 35.9 ± 1.3 36.8 ± 1.5Glucose 4.25% 59.8 ± 1.6 60.5 ± 1.7 59.1 ± 1.6

Results are expressed as mean (n=3)±S.D.

Glucose at all concentrations used causes an increase in intraperitonealfluid volume which is completed in the first 2 h. In fact, at 4 and 6 hthe fluid volume in the peritoneum remains constant.

The same experiment was conducted using scalar concentrations ofcarnitine. The results are given in Table 3.

TABLE 3 Percentage changes in fluid volume recovered from rats submittedto peritoneal dialysis with 15 ml of solution containing differentconcentrations of carnitine. % increase in % increase in % increase involume volume volume Solutions (2 h) (4 h) (6 h) Carnitine 1.5% 25.8 ±1.3 22.5 ± 1.6 25.3 ± 1.4 Carnitine 2.5% 38.1 ± 1.4 37.3 ± 1.4 38.5 ±1.6 Carnitine 4.25% 61.5 ± 1.5 64.1 ± 1.8 62.3 ± 1.9

Results are expressed as mean (n=3)±S.D.

Carnitine, too, proves to be a good osmotic agent, at least as good asglucose. The percentage increase in intraperitoneal fluid volume isslightly greater than that produced by glucose. The fluid recovery bythe solution containing carnitine is also rapid in this case and reachespeak activity within 2 h, producing no further increases in volume atthe later observation times (4, 6 h).

After confirming the activity of carnitine as an osmotic agent forperitoneal dialysis in vivo, we conducted a series of experiments usingcarnitine in mixtures with glucose or amino acids (aa), maintaining thetotal percentage of osmolites equal to 1.5%. The results are summarizedin Table 4.

Table 5, on the other hand, gives the composition of the amino acidsused. The composition of the amino acid solution is the optimalcomposition to minimize the metabolic acidosis that may occur when suchsolutions are used.

TABLE 4 Percentage changes in fluid volume recovered from rats submittedto peritoneal dialysis with 15 ml of solution containing differentmixtures of carnitine, glucose and amino acids (aa). % increase in %increase in % increase in volume volume volume Solutions (2 h) (4 h) (6h) Carnitine 1.5% 25.8 ± 1.3 22.5 ± 1.6 25.3 ± 1.4 Glucose 1.5% 21.1 ±1.5 21.5 ± 1.9 21.7 ± 1.6 Car + Glu 1.0 + 0.5% 25.6 ± 1.6 28.4 ± 1.627.6 ± 1.5 Car + aa 0.5 + 1.0% 24.6 ± 1.2 26.4 ± 1.3 25.3 ± 1.2 Car + aa0.8 + 0.7% 23.1 ± 1.5 24.5 ± 1.4 26.0 ± 1.5 Car + aa 1.0 + 0.5% 25.9 ±1.5 28.4 ± 1.5 33.8 ± 1.4

Results are expressed as mean (n=3)±S.D.

The fluid recovery in the first 2 h is comparable for all solutionsassayed and ranges from 21.7 to 25.9%. Moreover, this increase remainsconstant at the later observation times (4 and 6 h) for all solutions,except for a tendency to increase over time in the case of the solutioncontaining Car+aa (1.0+0.5%).

TABLE 5 Composition of solution containing aa Concentration Amino acids(mg %) Leucine  74-112 Valine 100-151 Threonine 47-71 Isoleucine 61-92Lysine HCl 55-83 Histidine 52-78 Methionine 32-48 Phenylalanine 42-62Tryptophan 20-30 Alanine  68-103 Proline 43-65 Arginine  60-113 Glycine36-55 Serine 48-72 Tyrosine 20-35 Aspartate 55-83 Glutamate 55-83Phenylalanine/Tyrosine 1.3-3.0 Generating/neutralizing acids   1-2.2Essential/Total 0.4-0.7

The following examples further illustrate the invention.

EXAMPLE 1

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Calcium 1.75 mmol/l Magnesium 0.5 mmol/l Chloride103.5 mmol/l Bicarbonate 34.0 mmol/l L-carnitine 1.5%

EXAMPLE 2

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Calcium 1.75 mmol/l Magnesium 0.5 mmol/l Chloride103.5 mmol/l Bicarbonate 34.0 mmol/l L-carnitine 2.5%

EXAMPLE 3

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Calcium 1.75 mmol/l Magnesium 0.5 mmol/l Chloride103.5 mmol/l Bicarbonate 34.0 mmol/l L-carnitine 4.25%

EXAMPLE 4

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Calcium 1.75 mmol/l Magnesium 0.5 mmol/l Chloride103.5 mmol/l Lactate 35.0 mmol/l L-carnitine 1.0% Glucose 0.5%

EXAMPLE 5

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Calcium 1.75 mmol/l Magnesium 0.5 mmol/l Chloride103.5 mmol/l Bicarbonate 34.0 mmol/l L-carnitine 1.0%

Mixture of Amino acids as in Table 5 0.5%

EXAMPLE 6

Solution for twin-bag peritoneal analysis

Bag 1 Sodium 193.0 mmol/l Calcium 1.75 mmol/l Magnesium 0.5 mmol/lChloride 103.5 mmol/l Lactate 35.0 mmol/l Glucose 0.5-4.0% Bag 2Bicarbonate 34.0 mmol/l L-carnitine 4.0-0.5%

EXAMPLE 7

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Potassium 2.0 mmol/l Calcium 1.75 mmol/l Magnesium0.5 mmol/l Chloride 105.5 mmol/l Bicarbonate 34.0 mmol/l L-carnitine1.5-4.25%

EXAMPLE 8

Solution for peritoneal dialysis

Sodium 134.0 mmol/l Potassium 2.0 mmol/l Calcium 1.75 mmol/l Magnesium0.5 mmol/l Chloride 105.5 mmol/l Lactate 35.0 mmol/l L-carnitine0.5-4.0% Glucose 4.0-0.5%

What is claimed is:
 1. A method of using L-carnitine and/or its alkanoylderivatives in peritoneal dialysis comprising administering to a subjecta solution comprising about 0.5% w/v to about 10% w/v of L-carnitineand/or its alkanoyl derivatives, in which the alkanoyl is a straight orbranched aliphatic group, with 2 to 8 carbon atoms, optionally in theform of a pharmaceutically acceptable salt, as an osmotic agent.
 2. Themethod according to claim 1, in which said osmotic agent is L-carnitine.3. The method according to claim 1, in which said osmotic agent isacetyl L-carnitine.
 4. The method according to claim 1, where saidosmotic agent is a combination of L-carnitine and at least one of itsalkanoyl derivatives.
 5. The method according to claim 4, in which saidalkanoyl derivative is acetyl L-carnitine.
 6. The method according toclaim 1, in which at least one additional osmotic agent is present inthe solution.
 7. The method according to claim 1, in which glucose isalso present in the solution.
 8. The method of claim 2, in which thesolution contains about 0.7 to about 7% w/v L-carnitine.
 9. The methodof claim 2, in which the solution contains about 1 to about 5% w/vL-carnitine.
 10. The method of claim 2, in which the solution containsabout 0.5% w/v L-carnitine.
 11. The method of claim 2, in which thesolution contains about 2.5% w/v L-carnitine.
 12. The method of claim 2,in which the solution contains about 4.25% w/v L-carnitine.
 13. Themethod of claim 7, in which the solution contains about 0.5% glucose andabout 1.0% w/v L-carnitine.